Sudan has "de facto expelled" a senior United Nations humanitarian affairs official after refusing to renew his "stay permit" for another year, the UN said on Sunday.

The foreign ministry informed the UN in Sudan that the annual permit for Ivo Freijsen, who heads the Sudan office of the UN Office for the Coordination of Humanitarian Affairs (Ocha), will not be renewed when it expires on June 6, the statement said.

"This is despite the request for a 12-month extension of his stay permit... which was submitted on 10 April 2016," it said, adding that the ministry did not provide an explanation in writing for its decision.

"The action by the government of Sudan is inconsistent with the fundamental principles of the international civil service enshrined in the Charter of the United Nations... to which Sudan is a party."

Mr Freijsen, who is Dutch, is the fourth senior UN official to be expelled from Sudan over the past two years, the statement said.

His expulsion comes in addition to the "forced closure of international NGO Tearfund in December 2015 and the de facto expulsion of three international NGO country representatives in recent months", it said.

Ocha in Sudan regularly highlights the humanitarian situation in war-torn areas such as Darfur, where a conflict since 2003 has left tens of thousands of people dead and about 2.5 million displaced, according to UN figures.

It also monitors South Sudanese refugees who flee to Sudan from war and food shortages in their country.

In its latest weekly bulletin, Ocha said that more than 69,000 South Sudanese had arrived in Sudan since January, the majority taking refuge in East Darfur.